From 14b240af8fef269d2c1d5dde2fff192b656c50f3 Mon Sep 17 00:00:00 2001 From: Michael Muré Date: Sun, 20 Jan 2019 15:41:27 +0100 Subject: identity: more cleaning and fixes after a code review --- .../google/go-cmp/cmp/internal/diff/diff.go | 363 --------------------- 1 file changed, 363 deletions(-) delete mode 100644 vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go (limited to 'vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go') diff --git a/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go b/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go deleted file mode 100644 index 260befea..00000000 --- a/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go +++ /dev/null @@ -1,363 +0,0 @@ -// Copyright 2017, The Go Authors. All rights reserved. -// Use of this source code is governed by a BSD-style -// license that can be found in the LICENSE.md file. - -// Package diff implements an algorithm for producing edit-scripts. -// The edit-script is a sequence of operations needed to transform one list -// of symbols into another (or vice-versa). The edits allowed are insertions, -// deletions, and modifications. The summation of all edits is called the -// Levenshtein distance as this problem is well-known in computer science. -// -// This package prioritizes performance over accuracy. That is, the run time -// is more important than obtaining a minimal Levenshtein distance. -package diff - -// EditType represents a single operation within an edit-script. -type EditType uint8 - -const ( - // Identity indicates that a symbol pair is identical in both list X and Y. - Identity EditType = iota - // UniqueX indicates that a symbol only exists in X and not Y. - UniqueX - // UniqueY indicates that a symbol only exists in Y and not X. - UniqueY - // Modified indicates that a symbol pair is a modification of each other. - Modified -) - -// EditScript represents the series of differences between two lists. -type EditScript []EditType - -// String returns a human-readable string representing the edit-script where -// Identity, UniqueX, UniqueY, and Modified are represented by the -// '.', 'X', 'Y', and 'M' characters, respectively. -func (es EditScript) String() string { - b := make([]byte, len(es)) - for i, e := range es { - switch e { - case Identity: - b[i] = '.' - case UniqueX: - b[i] = 'X' - case UniqueY: - b[i] = 'Y' - case Modified: - b[i] = 'M' - default: - panic("invalid edit-type") - } - } - return string(b) -} - -// stats returns a histogram of the number of each type of edit operation. -func (es EditScript) stats() (s struct{ NI, NX, NY, NM int }) { - for _, e := range es { - switch e { - case Identity: - s.NI++ - case UniqueX: - s.NX++ - case UniqueY: - s.NY++ - case Modified: - s.NM++ - default: - panic("invalid edit-type") - } - } - return -} - -// Dist is the Levenshtein distance and is guaranteed to be 0 if and only if -// lists X and Y are equal. -func (es EditScript) Dist() int { return len(es) - es.stats().NI } - -// LenX is the length of the X list. -func (es EditScript) LenX() int { return len(es) - es.stats().NY } - -// LenY is the length of the Y list. -func (es EditScript) LenY() int { return len(es) - es.stats().NX } - -// EqualFunc reports whether the symbols at indexes ix and iy are equal. -// When called by Difference, the index is guaranteed to be within nx and ny. -type EqualFunc func(ix int, iy int) Result - -// Result is the result of comparison. -// NSame is the number of sub-elements that are equal. -// NDiff is the number of sub-elements that are not equal. -type Result struct{ NSame, NDiff int } - -// Equal indicates whether the symbols are equal. Two symbols are equal -// if and only if NDiff == 0. If Equal, then they are also Similar. -func (r Result) Equal() bool { return r.NDiff == 0 } - -// Similar indicates whether two symbols are similar and may be represented -// by using the Modified type. As a special case, we consider binary comparisons -// (i.e., those that return Result{1, 0} or Result{0, 1}) to be similar. -// -// The exact ratio of NSame to NDiff to determine similarity may change. -func (r Result) Similar() bool { - // Use NSame+1 to offset NSame so that binary comparisons are similar. - return r.NSame+1 >= r.NDiff -} - -// Difference reports whether two lists of lengths nx and ny are equal -// given the definition of equality provided as f. -// -// This function returns an edit-script, which is a sequence of operations -// needed to convert one list into the other. The following invariants for -// the edit-script are maintained: -// • eq == (es.Dist()==0) -// • nx == es.LenX() -// • ny == es.LenY() -// -// This algorithm is not guaranteed to be an optimal solution (i.e., one that -// produces an edit-script with a minimal Levenshtein distance). This algorithm -// favors performance over optimality. The exact output is not guaranteed to -// be stable and may change over time. -func Difference(nx, ny int, f EqualFunc) (es EditScript) { - // This algorithm is based on traversing what is known as an "edit-graph". - // See Figure 1 from "An O(ND) Difference Algorithm and Its Variations" - // by Eugene W. Myers. Since D can be as large as N itself, this is - // effectively O(N^2). Unlike the algorithm from that paper, we are not - // interested in the optimal path, but at least some "decent" path. - // - // For example, let X and Y be lists of symbols: - // X = [A B C A B B A] - // Y = [C B A B A C] - // - // The edit-graph can be drawn as the following: - // A B C A B B A - // ┌─────────────┐ - // C │_|_|\|_|_|_|_│ 0 - // B │_|\|_|_|\|\|_│ 1 - // A │\|_|_|\|_|_|\│ 2 - // B │_|\|_|_|\|\|_│ 3 - // A │\|_|_|\|_|_|\│ 4 - // C │ | |\| | | | │ 5 - // └─────────────┘ 6 - // 0 1 2 3 4 5 6 7 - // - // List X is written along the horizontal axis, while list Y is written - // along the vertical axis. At any point on this grid, if the symbol in - // list X matches the corresponding symbol in list Y, then a '\' is drawn. - // The goal of any minimal edit-script algorithm is to find a path from the - // top-left corner to the bottom-right corner, while traveling through the - // fewest horizontal or vertical edges. - // A horizontal edge is equivalent to inserting a symbol from list X. - // A vertical edge is equivalent to inserting a symbol from list Y. - // A diagonal edge is equivalent to a matching symbol between both X and Y. - - // Invariants: - // • 0 ≤ fwdPath.X ≤ (fwdFrontier.X, revFrontier.X) ≤ revPath.X ≤ nx - // • 0 ≤ fwdPath.Y ≤ (fwdFrontier.Y, revFrontier.Y) ≤ revPath.Y ≤ ny - // - // In general: - // • fwdFrontier.X < revFrontier.X - // • fwdFrontier.Y < revFrontier.Y - // Unless, it is time for the algorithm to terminate. - fwdPath := path{+1, point{0, 0}, make(EditScript, 0, (nx+ny)/2)} - revPath := path{-1, point{nx, ny}, make(EditScript, 0)} - fwdFrontier := fwdPath.point // Forward search frontier - revFrontier := revPath.point // Reverse search frontier - - // Search budget bounds the cost of searching for better paths. - // The longest sequence of non-matching symbols that can be tolerated is - // approximately the square-root of the search budget. - searchBudget := 4 * (nx + ny) // O(n) - - // The algorithm below is a greedy, meet-in-the-middle algorithm for - // computing sub-optimal edit-scripts between two lists. - // - // The algorithm is approximately as follows: - // • Searching for differences switches back-and-forth between - // a search that starts at the beginning (the top-left corner), and - // a search that starts at the end (the bottom-right corner). The goal of - // the search is connect with the search from the opposite corner. - // • As we search, we build a path in a greedy manner, where the first - // match seen is added to the path (this is sub-optimal, but provides a - // decent result in practice). When matches are found, we try the next pair - // of symbols in the lists and follow all matches as far as possible. - // • When searching for matches, we search along a diagonal going through - // through the "frontier" point. If no matches are found, we advance the - // frontier towards the opposite corner. - // • This algorithm terminates when either the X coordinates or the - // Y coordinates of the forward and reverse frontier points ever intersect. - // - // This algorithm is correct even if searching only in the forward direction - // or in the reverse direction. We do both because it is commonly observed - // that two lists commonly differ because elements were added to the front - // or end of the other list. - // - // Running the tests with the "debug" build tag prints a visualization of - // the algorithm running in real-time. This is educational for understanding - // how the algorithm works. See debug_enable.go. - f = debug.Begin(nx, ny, f, &fwdPath.es, &revPath.es) - for { - // Forward search from the beginning. - if fwdFrontier.X >= revFrontier.X || fwdFrontier.Y >= revFrontier.Y || searchBudget == 0 { - break - } - for stop1, stop2, i := false, false, 0; !(stop1 && stop2) && searchBudget > 0; i++ { - // Search in a diagonal pattern for a match. - z := zigzag(i) - p := point{fwdFrontier.X + z, fwdFrontier.Y - z} - switch { - case p.X >= revPath.X || p.Y < fwdPath.Y: - stop1 = true // Hit top-right corner - case p.Y >= revPath.Y || p.X < fwdPath.X: - stop2 = true // Hit bottom-left corner - case f(p.X, p.Y).Equal(): - // Match found, so connect the path to this point. - fwdPath.connect(p, f) - fwdPath.append(Identity) - // Follow sequence of matches as far as possible. - for fwdPath.X < revPath.X && fwdPath.Y < revPath.Y { - if !f(fwdPath.X, fwdPath.Y).Equal() { - break - } - fwdPath.append(Identity) - } - fwdFrontier = fwdPath.point - stop1, stop2 = true, true - default: - searchBudget-- // Match not found - } - debug.Update() - } - // Advance the frontier towards reverse point. - if revPath.X-fwdFrontier.X >= revPath.Y-fwdFrontier.Y { - fwdFrontier.X++ - } else { - fwdFrontier.Y++ - } - - // Reverse search from the end. - if fwdFrontier.X >= revFrontier.X || fwdFrontier.Y >= revFrontier.Y || searchBudget == 0 { - break - } - for stop1, stop2, i := false, false, 0; !(stop1 && stop2) && searchBudget > 0; i++ { - // Search in a diagonal pattern for a match. - z := zigzag(i) - p := point{revFrontier.X - z, revFrontier.Y + z} - switch { - case fwdPath.X >= p.X || revPath.Y < p.Y: - stop1 = true // Hit bottom-left corner - case fwdPath.Y >= p.Y || revPath.X < p.X: - stop2 = true // Hit top-right corner - case f(p.X-1, p.Y-1).Equal(): - // Match found, so connect the path to this point. - revPath.connect(p, f) - revPath.append(Identity) - // Follow sequence of matches as far as possible. - for fwdPath.X < revPath.X && fwdPath.Y < revPath.Y { - if !f(revPath.X-1, revPath.Y-1).Equal() { - break - } - revPath.append(Identity) - } - revFrontier = revPath.point - stop1, stop2 = true, true - default: - searchBudget-- // Match not found - } - debug.Update() - } - // Advance the frontier towards forward point. - if revFrontier.X-fwdPath.X >= revFrontier.Y-fwdPath.Y { - revFrontier.X-- - } else { - revFrontier.Y-- - } - } - - // Join the forward and reverse paths and then append the reverse path. - fwdPath.connect(revPath.point, f) - for i := len(revPath.es) - 1; i >= 0; i-- { - t := revPath.es[i] - revPath.es = revPath.es[:i] - fwdPath.append(t) - } - debug.Finish() - return fwdPath.es -} - -type path struct { - dir int // +1 if forward, -1 if reverse - point // Leading point of the EditScript path - es EditScript -} - -// connect appends any necessary Identity, Modified, UniqueX, or UniqueY types -// to the edit-script to connect p.point to dst. -func (p *path) connect(dst point, f EqualFunc) { - if p.dir > 0 { - // Connect in forward direction. - for dst.X > p.X && dst.Y > p.Y { - switch r := f(p.X, p.Y); { - case r.Equal(): - p.append(Identity) - case r.Similar(): - p.append(Modified) - case dst.X-p.X >= dst.Y-p.Y: - p.append(UniqueX) - default: - p.append(UniqueY) - } - } - for dst.X > p.X { - p.append(UniqueX) - } - for dst.Y > p.Y { - p.append(UniqueY) - } - } else { - // Connect in reverse direction. - for p.X > dst.X && p.Y > dst.Y { - switch r := f(p.X-1, p.Y-1); { - case r.Equal(): - p.append(Identity) - case r.Similar(): - p.append(Modified) - case p.Y-dst.Y >= p.X-dst.X: - p.append(UniqueY) - default: - p.append(UniqueX) - } - } - for p.X > dst.X { - p.append(UniqueX) - } - for p.Y > dst.Y { - p.append(UniqueY) - } - } -} - -func (p *path) append(t EditType) { - p.es = append(p.es, t) - switch t { - case Identity, Modified: - p.add(p.dir, p.dir) - case UniqueX: - p.add(p.dir, 0) - case UniqueY: - p.add(0, p.dir) - } - debug.Update() -} - -type point struct{ X, Y int } - -func (p *point) add(dx, dy int) { p.X += dx; p.Y += dy } - -// zigzag maps a consecutive sequence of integers to a zig-zag sequence. -// [0 1 2 3 4 5 ...] => [0 -1 +1 -2 +2 ...] -func zigzag(x int) int { - if x&1 != 0 { - x = ^x - } - return x >> 1 -} -- cgit